Yup, the hand cannon really fires....it's also the most powerful "gun" in the game by far.
Kills any standard, elite (black) necro with one shot -tripods/parasite carriers usually need two. The final boss fight with Nicole/Marker took about 3 seconds, as opposed to using a fully specced up Contact Beam on Hard Core which took around 12-15 seconds

Shooting the hand cannon, Isaac says "bang", alternate fire Isaac says "pew". I assume the Hand Cannon was a game development tool. The only thing it's probably not the best for is the groups of little parasites ( Force Gun or just stasis and stomp), and the Detonator still comes in handy for the container rooms with the stalkers (the velociraptor looking necro's)

Hard Core is a little easier to play than Zealot (necro's are slightly weaker on Hard Core)- just the lack of save points.